Process for the concurrent recovery of acid and metal values from spent pickle acid containing the same

ABSTRACT

A process for the concurrent recovery of acid and metal values from spent pickle acid containing the same which comprises: A. ADDING A QUANTITY OF SULFURIC ACID TO THE SPENT PICKLE ACID OTHER THAN SULFURIC ACID AT LEAST SUFFICIENT TO CONVERT THE SOLUBLE SALTS IN THE PICKLE ACID TO SOLUBLE METAL SULFATES AND AT THE SAME TIME, REGENERATE THE PICKLE ACID; B. RECOVERING THE PURE PICKLE ACID BY DISTILLATION; C. OXIDIZING THE SOLUBLE METAL SULFATES IF IRON SULFATE IS PRESENT TO INSOLUBLE METAL HYDROXIDES; D. NEUTRALIZING ANY EXCESS SULFURIC ACID WHICH MAY BE PRESENT WITH A BASE TO FORM AN INSOLUBLE METAL SULFATE; E. ADDING A QUANTITY OF SULFURIC ACID SUFFICIENT TO CONVERT THE INSOLUBLE METAL HYDROXIDES OTHER THAN FERRIC HYDROXIDE WHICH MAY BE PRESENT TO SOLUBLE SULFATE SALTS; F. REMOVING THE INSOLUBLE FERRIC HYDROXIDE AND/OR INSOLUBLE METAL SULFATE, IS PRESENT, BY FILTRATION TO RESULT IN A FILTRATE CONTAINING IRON-FREE SOLUBLE METAL SULFATES; G. ADJUSTING THE PH and the concentration of the filtrate to that suitable for an electroplating solution; and H. RECOVERING THE METALS FROM THE ELECTROPLATING SOLUTION BY ELECTROLYSIS.

ite States Patent 1 Senior et a1.

[ Jan. 22, 1974 PROCESS FOR THE CONCURRENT RECOVERY OF ACID AND METALVALUES FROM SPENT PICKLE ACID CONTAINING THE SAME Inventors: Franklin C.Senior, Phoenix, Ariz.; Douglas MacGregor, Murray, Utah [73] Assignee:Cationic Corporation, New York,

Filed: Oct. 20, 1971 Appl. No.2 190,882

References Cited UNITED STATES PATENTS 5/1956 Wunderley 423/166 10/1928Lofland 423/633 7/1915 Hoffman 423/633 1,565,215 l2/l925 Smith 423/1061,415,797 5/1922 Christensen 423/106 FOREIGN PATENTS OR APPLICATIONS992,767 5/1965 Great Britain 204/122 OTHER PUBLICATIONS Metal FinishingGuidebook, 1968, pgs. 244, 264, 300, 369.

Handbook of Chemistry & Physics, 32nd ed., 1950, pgs. 506507.

Primary ExaminerJohn H. Mack Assistant Examiner-R. L. Andrews Attorney,Agent, or Firm-Pennie & Edmonds [5 7] ABSTRACT A process for theconcurrent recovery of acid and metal values from spent pickle acidcontaining the same which comprises:

a. adding a quantity of sulfuric acid to the spent pickle acid otherthan sulfuric acid at least sufficient to convert the soluble salts inthe pickle acid to soluble metal sulfates and at the same time,regenerate the pickle acid;

b. recovering the pure pickle acid by distillation;

c. oxidizing the soluble metal sulfates if iron sulfate is present toinsoluble metal hydroxides;

d. neutralizing any excess sulfuric acid which may be present with abase to form an insoluble metal sulfate;

e. adding a quantity of sulfuric acid sufficient to convert theinsoluble metal hydroxides other than ferric hydroxide which may bepresent to soluble sulfate salts;

f. removing the insoluble ferric hydroxide and/or insoluble metalsulfate, is present, by filtration to result in a filtrate containingiron-free soluble metal sulfates;

g. adjusting the pH and the concentration of the filtrate to thatsuitable for an electroplating solution; and

h. recovering the metals from the electroplating solution byelectrolysis.

13 Claims, 2 Drawing Figures l0 2 l3 1 l f w l l r lrlC c1 Evo Coniigflqg'g orot r denser 1 to es P h ed i u Purified, g g l4 Strengthenedm H1105 for Recycle H2804 HN 0a l I A Sulfuric l5 PurchasedCrystollizer/ H2504 -=1Woter Converter Tank 1 5' F 23 Mother lilquor 192| l-% 22 28 on r 1 Woter IO 7 W 1 2o Crysto l l lzer/ g r f f EvqtpdCon- Converter 2?, on olnmg ore or enser 5 Cu and Be B E ii'lili'iiiSulfates 26 g Beryllium 3Q I er Extraction/ 24 0 ewer Unit Crystollizer/gg-"gz'yzwag Decuntor fig u Electl I Tank Sulfate W 27 rolytic g 2 CellBACKGROUND OF THE INVENTION The making, shaping and finishing ofstainless, high alloy and super alloy steel, copper, beryllium and othermetals normally involves a pickling step in which the metals areimmersed in strong acid baths to remove oxidized surface scale in orderto place the metal in suitable condition for further processing andforming. In addition to the employment of various acids to clean andremove oxide and mill scale in stainless steel and other metalsproduction, most electroplating and galvanizing operations are requiredto discard many thousands of tons of acid a year which contain valuablemetal values such as nickel, chromium, silver, beryllium and copper. Theacids most commonly used for these purposes are among the most corrosiveand poisonous known, namely, sulfuric, nitric, nitrichydrofluoric andhydrochloric. The steel and metal plant acid pickle solutions may beused until their acid content is decreased by the formation of salts ofiron and other metals through the removal of mill scale and oxide. Atthis point, they must be discarded and fresh pickling acids used becauseof the acids reduced effectiveness in removing mill scale and oxide fromstainless steel and other alloy steels and metals. It has been foundthat such waste acid streams contain salts having approximately 3-10percent iron, 0.4-1.2 percent nickel, 3.5- percent chromium, 0.04-0.06percent cobalt and 0.1-0.2 percent zinc, 0.05l5.0 percent copper,0.01-0.04 percent beryllium and other metals.

Depending on the pickle acid used, the oxides or scale enters solutionin the acids as sulfates, chlorides, nitrates or fluorides. The ironoxide scale is at first an insoluble material. It is converted by theacid to a substantially soluble salt. In the case of iron, the ferricsalt which is derived from ferric oxide is reduced to the ferrous statewhich is substantially soluble in the pickle acid. The extent of the useof pickling acids in steel manufacture or production may be appreciatedby the fact that from 50 to 400 pounds of strong acid solutions are usedfor each ton of finished steel produced in this country. The typicalranges of the percent acid in the initial solutions are 20-50 percentfor nitric acid streams, l5-25 percent nitric plus 5 to percenthydrofluoric in nitric-hydrofluoric streams and 30-50 percent forhydrochloric streams, parts of which are converted to salts and sludges.The neutralization of waste acid streams of nitric, hydrochloric,hydrofluoric and nitric-hydrofluoric acids results in the production oflarge quantities of highly soluble salts. Discarcling these salts in theearth, streams, rivers, etc. has resulted in a serious level ofpollution and ecological disruption. In addition to the effect on theecology of these highly corrosive obnoxious acids and the salts of theseacids as they are dumped into the earth and into streams making themtoxic to all life, there is a great economic loss of 4-5 million dollarswhich is required to replace up to 200,000 tons of various acidsolutions which are annually consumed in pickling and electroplatingoperations. The spent waste acid streams may also be neutralized by theaddition of a base such as calcium or sodium hydroxide forming largequantities of obnoxious slude. In addition, it has been estimated thatin the production of a million tons of stainless steel there is a lossof 3 million pounds of nickel and cobalt in the waste acid streams.There is also a loss of some 8,000 tons of iron and several millionpounds of zinc, copper, beryllium, tungsten and chromium. The totalannual economic loss for the cost of new acids and the loss of metalvalues in the acids in the United States alone is conservatively 20million dollars a year.

SUMMARY OF THE INVENTION We have now discovered a method for treatinglarge volumes of spent acid streams other than sulfuric acid streams bythe controlled addition of sulfuric acid to convert the metallic saltsto soluble sulfates and the evaporation and condensation of the acid torecover the acid in a pure state and in a concentration which may behigher than original and suitable for recycling in the acid picklingoperations or for other uses. The method also provides for theconcurrent recovery of metallic values from the thus treated waste acidstreams and also from wet sludge and dry solid metal bearing wastes suchas baghouse dust rolling mill scale and grinding dusts through thedigestion of the sludge and dust with sulfuric acid to convert themetallic hydroxides and oxides to soluble sulfates, the oxidation andneutralization of the resulting solution to remove iron, chromium andcalcium compounds by filtration, controlling the dilution and the pH asrequired by the addition of suitable acids and bases to redissolve andrecover nickel, cobalt and copper valves and the electrolytic depositionof the metal values from the clear filtrate and the recycling, ifdesired, of the demetalllized sulfuric acid solution.

In addition to the recovery of acid and metal values from the waste acidstreams, the process of this invention eliminates the problemsassociated with the disposal of highly soluble, toxic salts since thesalts herein are ecologically harmless, substantially insoluble sulfatesalts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and 2 are schematic flow sheetseach illustrating an embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, storagetanks 10, 11 and 12 contain waste acids that are contaminated withsoluble metallic salts which have been obtained from steel plants orother metal pickling processes. Storage tank 11 holds a spenthydrochloric acid solution containing ferrous nickel chloride and othermetal salts. The hydrochloric acid solution stream is delivered by aone-half horsepower pump 13 through line 14 at a rate of several gallonsper minute to evaporator 15. Concentrated sulfuric acid is deliveredfrom tank 16 through line 17 to evaporator 15 to be mixed with the wastehydrochlo ric acid stream to convert the soluble ferrous chloride andother salts to soluble ferrous sulfates and ferric chloride to ferricsulfate. The concentrated sulfuric acid and metal sulfates contained inthe still bottoms are kept well under the fuming temperature of 600F inorder to capture and retain approximately 15 to 30 percent of the waterin the incoming hydrochloric acid stream. In this manner, thehydrochloric acid which is recovered from condenser 18 is advantageouslyconcentrated so that the acid which is delivered through line 19 forrecycling in pickling operations is a 20-25 percent acid solution orsubstantially stronger than the hydrochloric acid normally used in freshacid pickle baths in a typical steel mill.

Metal sulfates remain in solution in the still bottoms. Sincehydrochloric acid evaporates at atmospheric pressure at 230F, the 25percent hydrochloric acid solution that is returned through line 19 toacid tank 20 for reuse in new pickling operations is substantially freeof iron or other metallic compound contaminants.

The solution of sulfuric and metal sulfates contained in evaporator isthen pumped through line 21 to line 31 to be mixed with the spentsulfuric acid stream and then to digester unit 22.

Waste nitric-hydrofluoric acid solution is similarly pumped at a rate ofseveral gallons per minute from storage tank 12 by acid pump 23 throughline 24 to evaporator 25. As was the case with the hydrochloric acidstream, concentrated sulfuric acid is delivered from acid tank 16 and ismixed with the nitrichydrofluoric acid solution stream to convert metalnitrates and fluorides to soluble sulfates. Since nitric acid vaporizesat about 225F and hydrofluoric acid vaporizes at about 183F, both acidsboil off at evaporator 25 while leaving metal sulfates such as iron,nickel, copper and beryllium sulfates, which are stable up to 630F, insolution. The acid vapors are condensed at condensor 26 and pumped alongline 27 to acid tank 28. In place of waste nitric-hydrofluoric acid,storage tank 28 may contain waste nitric acid without altering theprocess of the present invention.

The metallic salt solution in evaporator 25 is fed through line 29 andis mixed with the waste sulfuric acid solution which has been pumpedfrom acid storage tank 10 by pump 30 at a rate of several gallons perminute through line 31 to digester 22.

In addition to the hydrochloric, sulfuric and nitrichydrofluoric acidstreams, waste wet sludge comprising about percent solid metalhydroxides may be introduced into digester unit 22 at a rate of 20 to 40tons per day. The gelatinous sludge results from the neutralization ofwaste acid streams with suitable bases and is performed by some steel ormetal plant operators. The gelatinous sludge contains ferric, nickel,copper and cobalt hydroxide and other salts of manganese, zinc andchromium.

The sludge is extremely difiicult or even impossible to filter anddewater to less than 20 percent solids contents and presentsconsiderable disposal problems for steel plants due to its vastaccumulation. It is usually discarded in a lagoon which results in theloss of significant amount of nickel, cobalt, iron, manganese, zinc andchromium. However, the solid hydroxides are readily solubilized andconverted to sulfates when they are introduced into the digestercontaining the confluence of two suluric acid and metal sulfate streamsfrom the stills and the sulfuric acid and metal sulfate stream from tank10. Concentrated sulfuric acid from holding tank 16 may also be pumpedinto the digester unit 22 to replace the sulfuric acid consumed by theformation of iron, chromium, calcium and other metallic sulfates. Theconversion to sulfates takes place at a pH of about 0.2 to L5. It hasbeen found in a typical operation that about 27 percent of the iron indigester 22 is in the ferrous state and about 73 percent of the iron ispresent as ferric or insoluble compounds.

Dry solid wastes consisting of mill scale, mill sludge, grinding dust orbaghouse dustcan also be treated and disposed of by the process of thepresent invention. Such dry solid wastes are more refractory than sludgeand require several hours of contact time with strong sulfuric acid inleach tower 32 before being added to the digester unit. The reaction isexothermic with a relatively large gas evolution, principally carbondioxide and steam, as the conversion to sulfates takes place. Therecycle leach tower 32 is provided with means to digest the severalhundred pounds per hour of dust for dissolution in the sulfuric stream,and to baffle the violent foaming that occasionally occurs.

The digested sulfate stream is pumped from digester 22 to oxidizing andneutralizing tank 33 which is subjected to sparging air at a rate ofseveral hundred cubic feet per minute and proper pressure to oxidize theferrous ions in solution to the ferric or insoluble state. Otheroxidizing agents such as hydrogen peroxide and nitric acid are alsosuitable for this purpose.

pH controller unit 34 feeds calcium hydroxide or other suitable base tocontrol and adjust pH during oxidation to a value advantageously fromabout 3 to 7. Advantageously, the base is a very finely ground powder ofabout 325 mesh and is carefully added as a slurry to prevent localdeposition of iron-nickel hydroxide. Advantageously, oxidation ispermitted to continue after the pH has reaced 4.0 in order to obtain acomplete oxidation of the ferrous ions for subsequent removal. At thispoint, concentrated sulfuric acid is carefully added to the solution toreduce the pH to about 3.0 to 3.5 to redissolve the nickel and coppercompounds. The solution is then filtered in vacuum filter 35 at asuitable rate. The insoluble ferric hydroxide and calcium sulfate isremoved with the filter cake and the clear filtrate containing thenickel and copper values is pumped to mother liquor tank 36. The motherliquor from tank 36 is extracted at a constant rate and delivered toplate filter 37 to remove the insoluble metal sulfates formed by theaddition of a corresponding metal hydroxide from pH meter 40 to controlthe pH of the electroplating solution.

The clear filtrate then passes to evaporator unit 38 where waterobtained from washing, sludge and incoming acids is removed and the purecondensate is passed to a sewer or recycled as wash water.

For example, a stream of about 3 gallons per minute carrying 88 poundsper hour of sulfates of nickel, cobalt, copper, etc., including 44pounds per hour in constant recycle, passing to electrolytic cell 39 forthe removal of copper results in a pure copper plate out substantiallyfree of nickel. The clear filtrate stream then passes to electrolyticcell 40 where nickel and cobalt are substantially removed from theplating circuit as cathode plates.

The depleted electrolyte has a lower pH due to the release of acid atthe cathode and is returned to the mother liquor tank 36.

pH control meter 41 is provided to feed milk of lime or other base tocontrol the pH of the plating solution in mother liquor tank 36 at asuitable pH.

Referring to FIG. 2, waste nitric acid in storage tank 10 contains byweight about 10 percent copper as oupric nitrate, about 0.20 berylliumas beryllium nitrate, about 8 percent free nitric acid and about 30percent combined metal salts. The waste nitric acid is fed through line11 at a suitable rate to evaporator unit 12 where a sufficient amount ofheat is applied to vaporize the free nitric acid and about 25 percent ofthe nitrate anion as nitric acid. The nitric acid vapors are condensedin 13 and are discharged through recycle line 14 at about 27-30 percent.Concentrated sulfuric acid made up with recycled sulfuric acid and/orpurchased acid is advantageously'added to evaporator 12 through line 11.The hot still bottoms in distillation unit 12 are discharged throughline 14 to crystallizer/converter tank 15. Sufficient amounts of water,concentrated sulfuric acid and sulfuric acid from evaporator 21 in therequired amounts are added to the hot still bottoms and the solution iscooled. The copper and beryllium sulfates thus formed settle to thebottom of tank 15 and are delivered through line 16 to mother liquortank 17. The supernatant, now containing regenerated nitric acid isdecanted from tank 15 and delivered thorugh line 18 to storage tank 10.

Tank 19 contains waste sulfuric acid containing about 3 percent copperand a small amount of beryllium as the sulfates thereof, as well asabout 20 percent free sulfuric acid. The waste acid is delivered throughline 20 to evaporator 21 where most of the water is evaporated andcondensed in 22. The water may be passed through line 23 to tank 15 orwithdrawn through line 24 to cyrstallizer/decantor tank 25. The hotstill bottoms in evaporator 21 containing sulfuric acid and metalsulfates is delivered to crystallizer/decantor tank 25 through line 26.Upon cooling of the still bottoms,

. the beryllium and copper sulfates crystallize and are deliveredthrough line 27 to mother liquor tank 17. The supernate containingconcentrated sulfuric acid is delivered to crystallizer/converter tank15 through line 28.

Mother liquor tank 17 now contains copper and beryllium sulfates.Suitable amounts of water and sulfuric acid are added to the sulfates toproduce the desired plating solution at a pH of from about 1.0-3.0. Thesolution in tank 17 is extracted with a suitable base, for example,hydrated lime and the calcium sulfate is filtered off at 29. The clearfiltrate then passes through a conventional liquid liquid berylliumberyllium extraction unit 30 where a suitable beryllium salt forexample, beryllium chloride is produced. The plating solution, nowcontaining only copper sulfate, is delivered to electrolytic cell 31where the copper is removed as a cathode plate or as a powder asdesired.

EXAMPLE 1 1,610 pounds per hour of waste hydrochloric acid pickle liquorhaving a specific gravity of 1.19 and containing about 8 percentmetallic chlorides was mixed with 220 pounds per hour of concentratedsulfuric acid in an evaporator/converter which was lined with teflon orother similar material. 1,460 pounds per hour of 25 percent by weight ofhydrochloric acid was distilled from this mixture and recycled for reusein pickling operations. At the same time, 1,470 pounds per hour of wastenitric-hydrofluoric acid pickle liquor and 200 pounds of concentratedsulfuric acid were mixed in a teflon lined evaporator/converter and1,240 pounds per hour of nitric-hydrofluoric acid having a specificgravity of 1.10 was distilled from this mixture and recycled for reusein pickling operations. A third waste pickle liquor stream of wastesulfuric acid was added to the residue of the distillation of both thehydrochloric and nitric hydrofluoric waste acid streams at the rate of350 pounds per hour and was delivered to the digester tank. Thehydrochloric waste acid stream was fed into the digester at the rate of370 pounds per hour and the residue of the nitric-hydrofluoricdistillation was fed into the digester at the rate of 430 pounds perhour for a total of 1,150 pounds per hour that was delivered to the6,000 gallon digester.

In addition, 2,500 pounds per hour of waste gelatinous nickel-ironhydroxide sludge was added to the digester. 140 pounds per hour of drydust, processed with lbs sulfuric acid, was also added to the digester.Di gestion and converstion to sulfates was accomplished at a pH of about0.2 to 1.5. The digested and converted sulfuric stream was thentransferred to a 3,000 gallon tank into which several hundred cubic feetper minute of air was introduced at 5 to 6 pounds per square inch for aperiod of three to six hours. A pH controller unit fed milk of lime intothe 3,000 gallon oxidizing and neutralizing tank to adjust the pH duringair oxidation from about 1.5 to about 7.0. 1,600 pounds of finely groundcalcium oxide was used during the six hour oxidizing neutralizing cycle.pounds of concentrated sulfuric acid was then introduced to lower the pHslowly to about 3.6 to redissolve the nickel and copper compounds. Thesolution in the oxidizing tank which contained approximately 262 poundsof nickel, cobalt and copper sulfate was filtered to remove ferrichydroxide and calcium sulfate and then the filtrate was transferred to a10,000 gallon holding tank. A controlling pH meter fed calcium oxideinto the 10,000 gallon holding tank to maintain pH at about less than 3to 3.5. Precipitated calcium sulfate was removed by a pressure filterand removed to the land fill. The filtrate was then transferred to anevaporator where 3,300 pounds of water were removed. The pure watercondensate was passed to the drain. The remaining sulfate filtrate wastransferred at a rate of 3 gallons per minute at a small 2 cathode 1,500ampere 2.5 volt cell where pure copper was plated out on the cathodesubstantially free of any nickel. The remaining sulfate solution wastransferred at a rate of 3 gallons per minute to a 20 cathodeelectrolytic cell having 4 feet by 4 feet cathode sheets and a capacityof 20,000 amperes and 10 volts. After removal of the nickel the depletedelectrolyte, having a decreased pH was transferred at a rate of 3gallons per minute back to the 10,000 gallon holding tank.

EXAMPLE 2 A procedure similar to that set forth in Example 1 wasfollowed except that the mother liquor in the crystallizer/decantor tankwas adjusted to a pH of about 10.0 with lime and the nickel and copperhydroxides thus formed settled to the bottom of the tank and werefiltered off. The filtrate and the supernate water were recycled. Thenickel and copper hydroxides were delivered to the mother liquor tankfor reconversion to soluble sulfates for plating. This procedureeliminated the need for evaporating the water from sludge washings andincoming acids.

EXAMPLE 3 11,350 pounds of nitric acid pickle waste containing 9 percentfree nitric acid by weight, 1,110 pounds of copper as copper nitrate andabout 18 pounds of beryllium as beryllium nitrate and some cobaltnitrate were delivered to a tank. The tank had previously contained5,680 pounds of a 30 percent by weight nitric acid stream from thedecantor tank. The mixture of 17,200 pounds were delivered to a smallstill where 12,200

pounds of a 27 percent pure nitric acid were evaporated and 3,700 poundsof still bottoms containing metal nitrates were delivered to theconverter/decanter tank. 1,270 pounds of sulfuric acid and 440 pounds ofreflux sulfuric acid from a companion still were added to this tank.

Simultaneously, 2,100 pounds of a waste sulfuric acid stream containingby weight, approximately 3.0 percent copper as copper sulfate, about 1pound of beryllium as beryllium sulfate and about 20 percent freesulfuric acid were delivered to a still where 1,180 pounds of water wereevaporated, condensed and refluxed to process.

The hot still bottoms, containing anhydrous copper sulfate and freesulfuric acid, were delivered to a small crystallizer/decantor tankwhere the copper sulfate settled upon cooling and the strong sulfuricacid supernate was decanted and delivered to the converter/decantor tanknoted above.

About 4,700 pounds of a hydrated copper sulfate from these tanks weredelivered to the 3,000 gallon mother liquor tank. 1,250 pounds ofsulfuric acid and 2,500 gallons of water were added to this tank toproduce the desired plating solution. pH of the plating solution wascontrolled by the addition of lime. The 2,000 pounds of insolublecalcium sulfate (gypsum) formed by lime addition was discarded.

The filtrate, containing beryllium and copper sulfates was delivered toa conventional liquid beryllium extractor unit. 156 pounds of berylliumchloride were recovered for recycling to the mill. The beryllium-freeplating liquid was delivered to the plating tanks and 1,170 pounds ofcopper plated out on the cathode for sale back to the mill or on theopen market.

The stripped plating solution was recycled back to the mother liquortank.

Analysis of the recycled nitric acid solution showed 27.0 percent byweight of nitric acid, 7 parts per million of copper, 1 part per millionof beryllium and no trace of cobalt.

EXAMPLE 4 1 1,300 pounds of nitric acid pickle waste containing aboutthe same quantities of components as in Example 3 were mixed with 2,000pounds of concentrated sulfuric acid and delivered to the evaporator.The sulfuric acid was made up of recovered sulfuric acid from the milland purchased acid.

The nitric acid recovered from the waste stream was 31 percent by weightand of high purity. The copper and beryllium sulfate still bottoms weretreated in a manner similar to Example 3 and 1,100 pounds of pure copperwere recovered as plate out on cathode starter sheets at 0.92 Kwhr/lband 1.8 volts.

We claim:

1. A process for the concurrent recovery of acid and metal values fromspent pickle acid containing the same which comprises:

a. adding a quantity of sulfuric acid to a spent pickle acid streamother than a spent sulfuric acid stream to convert the soluble metalsalts to soluble metal sulfates and at the same time, regenerate thepickle acid;

b. recovering the pickle acid by distillation;

c. oxidizing the soluble metal sulfates present in the distillationresidue resulting from step (b) to convert the soluble metal sulfates toinsoluble metal hydroxides;

d. neutralizing excess sulfuric acid present in the medium of step (c)with lime to adjust the pH from about 3 to 7 and to form metalhydroxides and calcium sulfate;

e. adding a quantity of sulfuric acid to the medium resulting from step(c) to lower the pH to about 3.0 to 3.5 to redissolve all of theinsoluble metal hydroxides except iron hydroxide;

f. removing the insoluble calcium sulfate and iron hydroxide byfiltration to provide a filtrate containing iron-free soluble metalsulfates;

g. adjusting the pH and the concentration of metal salts in the filtrateto that suitable for an electroplating solution; and

h. recovering the metal values from the solution of step (g) byelectroplating.

2. The process of claim 1 wherein the spent pickle acid is nitric acid,nitric-hydrofluoric acid or hydrochloric acid.

3. The process of claim 2 where in addition to iron, the spent pickleacid contains one or more metals in the form of a salt or salts of thewaste pickle acid, said metal selected to be copper, beryllium, nickel,chromium, cobalt or zinc.

4. The process of claim 1 wherein excess sulfuric acid is added at step(a) and the distillation step (b) is carried out well under the fumingtemperature of sulfuric acid.

5. The process of claim 1 wherein the oxidizing step is carried out withair, hydrogen peroxide or nitric acid as the oxidizing agent.

6. The process of claim 1 wherein the pH adjustment of step (g) iscarried out with sulfuric acid or lime.

7. A process for the concurrent recovery of acid and metal values fromspent pickle acid containing the same which comprises:

a. adding a quantity of sulfuric acid to a spent pickle acid streamother than a spent sulfuric acid stream to convert the soluble metalsalt or salts to soluble metal sulfates and at the same time, regeneratethe pickle acid;

b. recovering the pickle acid by distillation;

0. adding to the distillation residue of (b) which comprises a solutionof soluble metal sulfates; at least one member of the group consistingof an ironcontaining mill scale, mill sludge, grinding dust and baghousedust reacted with strong sulfuric acid, and insoluble metal hydroxideincluding iron hydroxide sludge;

d. digesting the insoluble metal hydroxides with sulfuric acid to formsoluble metal sulfates;

e. oxidizing the soluble metal sulfates to insoluble metal hydroxides;

f. neutralizing excess sulfuric acid present in the medium of step (e)with lime to adjust the pH from about 3 to 7 and to form metalhydroxides and calcium sulfate;

g. adding a quantity of sulfuric acid to the medium resulting from step(f) to lower the pH to about 3.0 to 3.5 to redissolve all of theinsoluble metal hydroxides except iron hydroxide;

h. removing the insoluble calcium sulfate and iron hydroxide byfiltration to provide a filtrate containing iron-free soluble metalsulfates.

i. adjusting the pH and the concentration of metal salts in the filtrateto that suitable for an electroplating solution; and

j. recovering the metal values from the solution of step (i) byelectroplating.

8. The process of claim 7 wherein the spent pickle acid is nitric acid,nitric-hydrofluoric acid or hydrochloric acid.

9. The process of claim 8 wherein the spent pickle acid contains one ormore metals in the form of a salt or salts of the waste pickle acid,said metal selected to be copper, beryllium, iron, nickel, chromium,cobalt or zinc, further provided, that when the metal is iron, at leastone other of the aforementioned metals is also present.

10. The process of claim 7 wherein excess sulfuric acid is added at step(a) and the distillation step (b) is carried out well under the fumingtemperature of sulfuric acid.

11. The process of claim 7 wherein the oxidizing step is carried outwith air, hydrogen peroxide or nitric acid as the oxidizing agent.

12. The process of claim 7, wherein the insoluble metal hydroxide addedin step (e) is iron hydroxide or a mixture of iron hydroxide and atleast one other hydroxide of nickel, cobalt, manganese, zinc orchromium. I

13. The process of claim 7 wherein the pH adjustment of step (h) iscarried out with sulfuric acid or lime.

2. The process of claim 1 wherein the spent pickle acid is nitric acid,nitric-hydrofluoric acid or hydrochloric acid.
 3. The process of claim 2where in addition to iron, the spent pickle acid contains one or moremetals in the form of a salt or salts of the waste pickle acid, saidmetal selected to be copper, beryllium, nickel, chromium, cobalt orzinc.
 4. The process of claim 1 wherein excess sulfuric acid is added atstep (a) and the distillation step (b) is carriEd out well under thefuming temperature of sulfuric acid.
 5. The process of claim 1 whereinthe oxidizing step is carried out with air, hydrogen peroxide or nitricacid as the oxidizing agent.
 6. The process of claim 1 wherein the pHadjustment of step (g) is carried out with sulfuric acid or lime.
 7. Aprocess for the concurrent recovery of acid and metal values from spentpickle acid containing the same which comprises: a. adding a quantity ofsulfuric acid to a spent pickle acid stream other than a spent sulfuricacid stream to convert the soluble metal salt or salts to soluble metalsulfates and at the same time, regenerate the pickle acid; b. recoveringthe pickle acid by distillation; c. adding to the distillation residueof (b) which comprises a solution of soluble metal sulfates; at leastone member of the group consisting of an iron-containing mill scale,mill sludge, grinding dust and baghouse dust reacted with strongsulfuric acid, and insoluble metal hydroxide including iron hydroxidesludge; d. digesting the insoluble metal hydroxides with sulfuric acidto form soluble metal sulfates; e. oxidizing the soluble metal sulfatesto insoluble metal hydroxides; f. neutralizing excess sulfuric acidpresent in the medium of step (e) with lime to adjust the pH from about3 to 7 and to form metal hydroxides and calcium sulfate; g. adding aquantity of sulfuric acid to the medium resulting from step (f) to lowerthe pH to about 3.0 to 3.5 to redissolve all of the insoluble metalhydroxides except iron hydroxide; h. removing the insoluble calciumsulfate and iron hydroxide by filtration to provide a filtratecontaining iron-free soluble metal sulfates. i. adjusting the pH and theconcentration of metal salts in the filtrate to that suitable for anelectroplating solution; and j. recovering the metal values from thesolution of step (i) by electroplating.
 8. The process of claim 7wherein the spent pickle acid is nitric acid, nitric-hydrofluoric acidor hydrochloric acid.
 9. The process of claim 8 wherein the spent pickleacid contains one or more metals in the form of a salt or salts of thewaste pickle acid, said metal selected to be copper, beryllium, iron,nickel, chromium, cobalt or zinc, further provided, that when the metalis iron, at least one other of the aforementioned metals is alsopresent.
 10. The process of claim 7 wherein excess sulfuric acid isadded at step (a) and the distillation step (b) is carried out wellunder the fuming temperature of sulfuric acid.
 11. The process of claim7 wherein the oxidizing step is carried out with air, hydrogen peroxideor nitric acid as the oxidizing agent.
 12. The process of claim 7,wherein the insoluble metal hydroxide added in step (e) is ironhydroxide or a mixture of iron hydroxide and at least one otherhydroxide of nickel, cobalt, manganese, zinc or chromium.
 13. Theprocess of claim 7 wherein the pH adjustment of step (h) is carried outwith sulfuric acid or lime.